Roofing sheets are generally supplied in rolled up form for use in the formation of roofing membranes wherein overlapping sections of the material are used to form one or more plies of the finished roofing membranes. In addition they may be used on sidewalls of buildings. Such roofing membranes and systems are used primarily on commercial buildings or buildings of low slope by reason of their durability and comparatively low cost. One type of roofing sheet which is in demand for economical installations is a thermoplastic styrene modified asphalt sheet. Roofing material modified with copolymeric styrene elastomers and rubbers are particularly in demand where some degree of flexibility is required, e.g. in built-up roofing to absorb the stresses during construction and to eliminate strain for the lifetime of the roof. However, a major disadvantage associated with the use of such copolymeric styrene modifiers is flammability, thus such modified asphalts do not provide roofing material having a required flame retardancey. Consequently, it has been the practice to manufacture the sheet with a glass mat reinforcement and to cover it with a separate flame retardant composition such as a glass cap sheet or coating. Obviously, this procedure requires several time consuming steps to complete the roofing installation. Therefore, it is an aim of research to simplify the process of manufacturing and installation of a fire resistant asphaltic roofing sheet. Several asphaltic compositions have been proposed which meet commercial specifications of char formation in a 90 second burn test but have failed the ASTM E-108 flame spread test required for commercial use and Class A rating.
Accordingly, it is an object of this invention to simplify the operation necessary for providing a fire retardant roofing membrane having a Class A rating.
Another object is to eliminate the necessity for a glass mat reinforcement either alone or in addition to the polyester reinforcment in the sheet and to provide a fire retardant roof covering with a material which incorporates fire retardancy, thus eliminating the need for membranes of different composition and top coating operations.
These and other objects will become apparent from those skilled in the art from the following description and disclosure.